(Photo: Reuters/Fort Worth Police Department/Handout via Reuters)Aaron Alexis, who the FBI believe to be responsible for the shootings at the Washington Navy Yard in the Southeast area of Washington, DC, is shown in this Fort Worth Police Department handout photo released on September 16, 2013. The 34-year-old gunman opened fire at the U.S. Navy Yard in Washington on Monday in a shooting that left 13 people dead at the busy military installation not far from the U.S. Capitol and the White House, officials said. Alexis of Fort Worth, Texas, was among the dead and authorities said they were searching for another possible gunman wearing military-style clothing.